1. Field of the Invention
The present invention relates to a method and apparatus for diagnosing a state of a fuel cell system, and more particularly to a method and apparatus for diagnosing in real time a state of a fuel cell system from a driving profile.
2. Description of the Related Art
A fuel cell vehicle typically includes a fuel cell stack in which includes a plurality of fuel cells, a fuel supply system which supplies hydrogen as a fuel to the fuel cell stack, an air supply system which supplies oxygen serving as an oxidant which is necessary for electrochemical reaction, and a water-and-heat management system which controls the temperature of the fuel cell stack.
The fuel cell system supplies compressed hydrogen in a hydrogen tank to a fuel electrode (anode) of the fuel cell stack by reducing the pressure of the hydrogen, and the air supply system supplies external air, which is blown in by operating an air blower, over an air electrode (cathode) of the fuel cell stack.
When hydrogen is supplied to the fuel electrode of the fuel cell stack and oxygen is supplied to the air electrode, hydrogen ions are produced through catalytic reaction. The hydrogen ions are transmitted, through an electrolyte membrane, to an oxidation electrode or air electrode. The hydrogen ions, electrons, and oxygen undergo electrochemical reaction at the oxidation electrode, thereby producing electric energy. More specifically, electrochemical oxidation of hydrogen occurs at the fuel electrode and electrochemical reduction of oxygen occurs at the air electrode. In this case, electricity and heat are produced due to movement of electrons, and vapor or water is produced through the electrochemical reaction of combining oxygen and hydrogen.
Additionally, in most systems, a discharging apparatus is provided to discharge byproducts such as vapor, water and heat which are produced when the fuel cell stack produces electrical energy, and unreacted gases such as remaining hydrogen and oxygen. Via the discharging apparatus, gases such as vapor, hydrogen, and oxygen are discharged into the atmosphere through an exhaust passage.
In theory, there are mainly two conditions that could contribute to dryout of a fuel cell stack. One condition is when the fuel cell vehicle is operating at a high temperature and high output, and the other is during low output. Dryout at high temperatures and high outputs is attributed to a collapse of heat balance in a fuel cell stack. Whereas, dryout at a low output is attributed to failure in supply of enough air, poor temperature control, and reduction in water production due to application of a low current and not running a load.
A dryout of a fuel cell stack results in reduction in the output of a fuel cell stack. Furthermore, it takes a long time to recover back to a normal output. Still furthermore, if the dryout continues for a long period of time, the performance of the fuel cell stack may be reduced to the extent that it is impossible to be recovered so that the fuel cell stack is likely to break down. Accordingly, a technique is needed to detect the dryout of a fuel cell stack and to perform an operation for recovering the fuel cell stack when the dryout is detected so that the fuel cell stack can recover easily from the dryout.
Although there are conventional methods of detecting the dryout of a fuel cell stack, such as Current Interrupt (CI) and Electrochemical Impedance Spectroscopy (EIS), these methods uses a specific current band, and thus are difficult to use in real time while the vehicle is operating. In addition, these methods are difficult to apply to a vehicle because additional high output hardware is necessary which would pass an additional cost onto the consumer.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.